The present invention relates to a new and improved construction of a tooth flank profile measuring apparatus for determining the roughness of a tooth flank surface.
In its more particular aspects the present invention specifically relates to a new and improved construction of a tooth flank profile measuring apparatus for determining the roughness of a tooth flank surface and which comprises a feeler rod or arm which is pivotably mounted in a housing and which carries at one end thereof a feeler or scanner tip for scanning the tooth flank surface, a measuring system generating signals which correspond to deflections of the feeler tip and which are supplied to an evaluation circuit, and further comprises a device for adjusting the bearing load of the feeler tip and acting upon the feeler rod or arm.
In a gear measuring machine as known, for example, from the MAAG brochure No. A-62-D3.81 and entitled "The New Gear Measuring Machine PH-40," see particularly pages 5 and 17 thereof, a surface feeler or scanner is mounted in the feeler or scanner holder of a feeler or scanner slide or carriage which otherwise receives the stylus or scanner for examining the involute shape of a tooth flank. In order to measure the roughness of the surface, the feeler or scanner tip of the surface feeler or scanner is applied to a tooth flank to be investigated; conventionally the feeler or scanner tip constitutes a diamond tip. The feeler or scanner tip scans the surface of the tooth flank. Deflections of the feeler or scanner tip are caused by the surface roughness and are detected by the measuring system which generally is connected to an indicating device via an evaluation circuit. In the known surface feeler or scanner there is used a piezo-electric measuring system and therein a rod of ceramic material is mechanically deformed due to the deflection of the feeler or scanner tip and thereby generates a signal which constitutes a piezo-electric voltage. The thus generated piezo-voltage is dependent on the deformation rate of the ceramic rod and, therefore, such piezo-electric systems have the disadvantage that slow-rate measuring movements or displacements cannot be received in the evaluation circuit without employing specific and complicated measures.
In further already known surface feelers or scanners an inductive carrier frequency system is used instead of the piezo-electric measuring system. The construction of such a known surface feeler or scanner is illustrated in FIG. 1 which is now referred to. A feeler rod or arm is generally designated by reference numeral 12 and this feeler rod or arm 12 is mounted in a housing, which is generally designated by reference numeral 10, by means of a cross-spring joint 14 such that the feeler rod or arm 12 is rotatable or pivotable about a fulcrum or point of rotation M which is located within the sectional plane of the illustration of FIG. 1. At one end, which is the left end in FIG. 1, the feeler rod or arm 12 is provided with a feeler or scanner tip 16 for scanning the surface of the flank of a not particularly illustrated gear. Two coils S1 and S2 with ferrite cup cores FS1 and FS2 are fixedly attached to a support body or member 18 which is secured in the housing 10. Ferrite cores F1 and F2 are fixedly attached to the feeler rod or arm 12 and each one of the ferrite cores F1 and F2 is arranged in an opposing relationship with respect to a related one of the ferrite cup cores FS1 and FS2. The coils S1 and S2 are connected via respective wires or leads L1 and L2 to an evaluation circuit 20 which is only schematically illustrated. An indicating device 22 is connected to the evaluation circuit 20. The surface feeler or scanner is illustrated in FIG. 1 in an excessively large scale; in reality the coils S1 and S2 have an outer diameter of only about 3 millimeters.
The internal structure of the evaluation circuit 20 is not shown in detail since the carrier frequency system used in the known surface feeler or scanner shown in FIG. 1 is generally known and of conventional structure. The evaluation circuit 20 for such carrier frequency system as shown in FIG. 1 contains a carrier frequency oscillator generating a carrier frequency voltage which is applied to the coils S1 and S2. The two coils S1 and S2 are arranged in the diagonal of a carrier frequency bridge system which is part of the evaluation circuit 20. During deflection of the feeler rod or arm 12 the air gap L between one of the coils S1 or S2 and the related ferrite core F1 or F2 is increased while the air gap formed between the other coil S2 or S1 and the related ferrite core F2 or F1 is reduced. The bridge circuit is thereby detuned and as a result a corresponding signal is generated. In the use of an inductive feeler or scanner system of the kind as illustrated in FIG. 1 there results the problem that the upper limiting or cut-off frequency is readily reached if it is intended to construct a fairly precise system using an acceptably complicated circuit. In the known feeler or scanner the coils S1 and S2 are operated at a carrier frequency in the range of 20 KHz. Theoretically a signal frequency in the range of 2 KHz can thus be achieved, i.e. a frequency response covering the range of 0 to 2 Khz.
A further problem in the surface feeler or scanner described hereinbefore results from the type of adjustment for the bearing load applied by the feeler or scanner tip. In order to ensure a defined bearing load of the feeler or scanner tip at all times, the feeler or scanner tip has to be biased relative to the flank surface which is to be investigated. For this purpose there are provided in the known feeler or scanner apparatus mounting bolts or screws B for the horizontal spring leaves or blades of the cross-spring joint 14. In order to adjust the bearing load, the mounting bolts or screws B are released and the feeler rod or arm 12 is forwardly displaced in a direction towards the feeler or scanner tip 16. During this operation the vertically extending spring leaf of the cross-spring joint 14 is bent in the forward direction. Consequently, and after re-tightening of the mounting bolts or screws B, the vertically extending spring leaf of the cross-spring joint 14 remains in the forwardly bent position and exerts a biasing force or bearing load upon the feeler rod or arm 12 and thus upon the feeler or scanner tip 16.
It is one of the major disadvantages of this type of adjusting of the biasing or bearing load that this force or load cannot be measured during the adjusting operation but only after the adjustment has been made. The correct adjustment of the force or load thus can only be found by experiments which represents a work-intensive operation. This problem is additionally aggravated by the fact that the size of the air gap L should have the best-defined possible size and a very small magnitude so that there is obtained the greatest possible control or operative range. This is only theoretically possible in the known feeler or scanner apparatus. A generally employed magnitude of the bearing load is in the range of 1.6 pond. In order to obtain such bearing load, the cross-spring joint 14 must be subjected to a spring bias which is at least thirty to fifty times as great. The considerable deformation or distortion of the cross-spring joint 14 required therefor results in a significant reduction in the mobility of the feeler rod or arm 12 which can have a very detrimental effect for the reasons stated hereinbelow.
The known surface feeler or scanner initially mentioned hereinabove contains a piezo-electric measuring system instead of the coil measuring system. Otherwise the piezo-electric measuring system essentially is of the same mechanical construction as the inductively operating feeler or scanner. A special driving or traversing apparatus is employed for a motor-driven reciprocation of the feeler or scanner tip in its engagement to the tooth flank. The driving or traversing apparatus contains a small-size motor and exchangeable bell-shaped curves or cams and the driving or traversing speed is selected such that the feeler rod or arm has sufficient mobility. When such a feeler or scanner system is inserted into the initially mentioned feeler or scanner holder, but without the driving or traversing apparatus, and when the same measuring drive or traversing means are used which are already present for profile testing in the tooth flank profile measuring apparatus, there results the problem that the mobility of the feeler rod or arm is insufficient. When the feeler or scanner tip actually scans the tooth flank in the region between the base of the tooth and the top land thereof, a change in the rate or speed results which corresponds to a ratio of about 1:4 although the gear rotates at a constant speed during the measurement. Additionally, the measuring rate can be changed by rotating the gear at higher speeds during the measurement which would correspond to a 1:20 ratio. Therefore high requirements are placed upon the surface feeler or scanner with respect to its frequency response, and thus, also with respect to its mobility, and such requirements cannot be fulfilled at all by the known surface feelers or scanners without the driving or traversing apparatus.